gpu: correctly target ~60hz, not 62,500hz, in Dawn example

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gpu/src/dawn/hello_triangle.zig

@@ -129,7 +129,7 @@ pub fn main() !void {
             .pipeline = pipeline,
             .queue = queue,
         });
-        std.time.sleep(16000);
+        std.time.sleep(16 * std.time.ns_per_ms);
     }
 }